The Fairy-Land of Science eBook

Even a short distance from the earth, however, at
the top of a high mountain, the air becomes lighter,
because it has less weight of atmosphere above it,
and people who go up in balloons often have great
difficulty in breathing, because the air is so thin
and light. In 1804 a Frenchman, named Gay-Lussac,
went up four miles and a half in a balloon, and brought
down some air; and he found that it was much less
heavy than the same quantity of air taken close down
to the earth, showing that it was much thinner, or
rarer, as it is called;* and when, in 1862, Mr. Glaisher
and Mr. Coxwell went up five miles and a half, Mr.
Glaisher’s veins began to swell, and his head
grew dizzy, and he fainted. The air was too
thin for him to breathe enough in at a time, and it
did not press heavily enough on the drums of his ears
and the veins of his body. He would have died
if Mr. Coxwell had not quickly let off some of the
gas in the balloon, so that it sank down into denser
air. (100 cubic inches near the earth weighed 31
grains, while the same quantity taken at four and
a half miles up in the air weighed only 12 grains,
or two-fifths of the weight.)

And now comes another very interesting question.
If the air gets less and less dense as it is farther
from the earth, where does it stop altogether?
We cannot go up to find out, because we should die
long before we reached the limit; and for a long time
we had to guess about how high the atmosphere probably
was, and it was generally supposed not to be more
than fifty miles. But lately, some curious bodies,
which we should have never suspected would be useful
to us in this way, have let us into the secret of
the height of the atmosphere. These bodies are
the meteors, or falling stars.

Most people, at one time or another, have seen what
looks like a star shoot right across the sky, and
disappear. On a clear starlight night you may
often see one or more of these bright lights flash
through the air; for one falls on an average in every
twenty minutes, and on the nights of August 9th and
November 13th there are numbers in one part of the
sky. These bodies are not really stars; they
are simply stones or lumps of metal flying through
the air, and taking fire by clashing against the atoms
of oxygen in it. There are great numbers of these
masses moving round and round the sun, and when our
earth comes across their path, as it does especially
in August and November, they dash with such tremendous
force through the atmosphere that they grow white-hot,
and give out light, and then disappear, melted into
vapour. Every now and then one falls to the earth
before it is all melted away, and thus we learn that
these stones contain tin, iron, sulphur, phosphorus,
and other substances.